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Full text of "Text Book Of Mechanical Engineering"

Appendix VI.

1015

CHAPTER IV.

P. JOG. The Power Hammer, so called because it is
actuated by mechanical power, rather than by steam or other
gas, is of considerable service for lighter forging in smiths' shops,
being made in various sizes from i Ib. to 5 cwt, but rarely
beyond the latter. As originally constructed (see 33, Fig. 317,
p. 349), the rotating shaft rocked a lever whose fulcrum could
be varied to alter the stroke and power of the blow; but the
present form depends entirely upon the adjustment of an air
cushion, the stroke of the lever being invariable.

The Longworth power-hammer as manufactured by Messrs.
Samuelson & Co., Figs. 926-7-8, will serve to illustrate the new
departure. Fig. 926 is a general view, and Fig. 927 a section
through the cylinders; and the same lettering is adopted
throughout. Fast and loose pullies are supplied at N, the
driving pulley being also a flywheel, to secure uniformity of
speed; and u is the striking gear for moving the belt fork v.
The rotation of the small crank P causes a connecting rod Q
to vibrate the bent lever R, which is further connected to the
upper or f actuating' cylinder by the coupling rods s s. This
cylinder is supplied with air holes at D and E ; and the piston A,
together with the rod A c and the tup, is therefore secondarily
moved up and down through the means of an air cushion
contained in D. On the upstroke the action is easily under-
stood, but on the downstroke it must be explained that the
cylinder D travels at a higher rate than that of the freely falling
tup, and gaining upon it, causes a sharper blow than would
otherwise occur. The lower and fixed cylinder B>is for* the
purpose of regulating the blow, or of preventing it altogether;
and this is effected by the valve K, which can be made to cover
any number of the ports at j, or to entirely open them. This
valve is worked by the attendant, either by hand at i, or by the
foot lever w and rod M, the release to the normal position of the
diagram (for complete inaction) being given by the long spring at M.

The working will now be easily understood. Putting the
belt upon the flywheel, the cylinder commences to move up and
down at 260 strokes per minute, but the tup never reaches the